1. Field of the Invention
The present invention relates generally to valves, and more particularly, but not by way of limitation, to an improved flow control valve for cooling towers.
2. Description of Related Art
Cooling towers of varying designs are widely used in industry for the purpose of removing waste heat from a process by natural evaporation of the cooling fluid, usually water. In operation, the hot water is piped from the process to the top of the cooling tower and distributed evenly using a system of distribution headers and valves. The outlet end of each valve is also attached to a distribution box which is disposed below and adjacent the water distribution header. The flow control valves function to divert the flow of water from the distribution header into the distribution box, as well as regulate the flow of water delivered to the distribution box. The distribution box functions to reduce the kinetic energy of the water as it flows out to fill the hot water basin. The deck of this basin is provided with a plurality of metering orifices patterned to distribute water evenly over a region provided with one of a variety of materials, known as "fill". The fill region is designed to provide a cooling surface to promote evaporative cooling. In this environment, each flow control valve regulates large volumes of fluid under relatively low pressures, in contrast to valves which regulate low volumes under high pressures.
The distribution header may contain a plurality of flow control valves to divert a large volume of fluid for evaporative cooling onto a plurality of hot water basins. The efficiency of the cooling tower is based on its ability to cool a volume of hot water. It is desirable that the hot water be evenly distributed into each of the hot water basins since each cell is capable of cooling only a certain volume of water through the designed temperature range. Thus, hot water distributed unevenly to the hot water basins reduces the efficiency of the cooling tower since some hot water basins cool the water quickly while other, more full basins, continue working to cool oversupplied volumes of hot water. Therefore, cooling tower efficiency greatly depends on even distribution of hot water from the distribution header by the flow control valves onto the respective hot water basins.
The flow control valves must be capable of complete shut-off to prevent leakage of water from the distribution header, particularly in freezing conditions. In cold weather, water from a leaking valve may collect through the fill region and freeze and eventually the excess weight could cause the cooling tower to collapse. However, the primary purpose of the valves is to divert and regulate the flow of water for even distribution, as compared to applications where valve use is limited to either complete "on" or "off" control.
Also, the flow control valves must be completely supported by the distribution header. Thermal expansion generates movement of the distribution header and the attached flow control valves. This movement can cause damage to a valve fixed to both the distribution header and the distribution box. Therefore, the flow control valves are attached to and completely supported by the distribution header with each valve outlet suspended over an opening in the distribution box. To better control the fluid flow from the valves, each valve outlet may be disposed in an opening in the distribution box and sealed in place with a flexible sealant. This provides a stable and seated mount while allowing the flow control valves to move as the distribution header expands and moves without damaging the valve mountings.
The high volume of fluid passes through the valve, even at low pressure, at a high velocity head. Impingement type valve design causes turbulent flow of the large volume of water passing through the valve which forces turbulent water to unevenly wear on the supports for the valve stem and plate. Also, impingement type valve devices have a high potential for failure under high velocity head conditions since impingement type valves use rubber gaskets which harden, crack and fail to provide a fluid-tight seal thereafter.
Generally, the plates of impingement type valves are completely backed-out until the plates are supported by the body of the valve which overcomes the unnecessary wear caused by the turbulent water flow. However, the valves are then incapable of regulating the flow of the fluid from the distribution header since the valves are completely open. This shortcoming of impingement type valves significantly decreases cooling tower efficiency, given the foregoing discussion of the importance of regulating the distribution of hot water.
Although existing plug type valves are aptly suited for cooling tower applications, the weight of these plug type valves, capable of handling such large volumes of fluid, is prohibitive for such an application. Since plug type valves operate differently than impingement type valves, there is no unnecessary wear from the high volume of fluid on the regulating elements. Also, the design of plug type valves enables fluid to flow in a near laminar state. Thus, this valve configuration minimizes turbulence of the high fluid volumes which is necessary for structural stabilization of the cooling tower components and improved control of fluid distribution.
To this end, a need exists for a lightweight plug type flow control valve for use, among other applications, for cooling towers. Such lightweight plug valve should provide near laminar flow of fluid and be capable of redirecting and regulating a large volume of fluid while capable of being completely open or shut in a fluid-tight position. It is to such a valve that the present invention is directed.